1. Field of the Invention
The invention is generally related to a process used in the fabrication of electrical components wherein electrical connections and mechanical connections are formed in the components in a single step.
2. Description of the Prior Art
For the past several years, efforts have been made to miniaturize electrical components such as circuit boards, semiconductor substrates and chips, ceramic packages, etc. A popular technique has been to create multilayered devices where each layer can contain circuit patterns and circuit devices. The circuit patterns and circuit devices on individual layers are interconnected by electrically conducting vias which pass through the individual layers. As miniaturization has progressed, fabricating the multilayered structures has become more complex, and circuitry and circuit devices have become increasingly more dense. A practical problem in creating multilayered devices which function properly is to assure that the layers remain connected together mechanically and that the circuitry and electrical components in the various layers remain connected electrically. Furthermore, connecting pins and other mechanical connectors to the connection pads on the multilayered devices has proved difficult because of the close spacing between the pads which results from dense circuitry.
U.S. Pat. No. 4,648,179 to Bhattacharyya et al. discloses a process for making a multilayered structure with interconnected electronic circuitry. Specifically, Bhattacharyya et al. disclose the fabrication of decal-like interconnection structures which include a central polymeric film, a circuit pattern formed on one surface of the polymeric film, metal filled vias created through the polymeric film connected to selected components of the circuit pattern, and a partially cured polymeric film located on the opposite surface of the polymeric film from the circuit pattern. The partially cured polymeric film is selectively removed from via areas to expose bonding metallurgy. The decal-like interconnection structures are then placed adjacent a substrate, such as a chip or the like, or adjacent other decal-like interconnection structures, with the exposed bonding metallurgy of the metal filled vias aligned with pads or circuitry of the adjacent substrate or decal-like interconnection structure. The entire package is then subjected to heat and compression to simultaneously form metal-to-metal, film-to-film, and film-to-substrate bonds. The polymeric films of the decal-like layers are directly bonded together by curing of the partially cured adhesive layer under temperature and pressure conditions in the press, and the finished structure resembles a thick polymeric film with circuitry positioned at varying levels within the film.
Japanese Application J6 0072-663-A discloses the use of solder balls to interconnect two printed circuit boards (PCBs). A protective sheet with a plurality of holes is positioned on a first PCB and solder balls with diameters larger than the holes are deposited in the holes in the protective sheet. A second PCB is then aligned with solder balls and electrically connected to the first PCB by applying heat to the combined structure.
U.S. Pat. No. 5,031,308 to Yamashita et al. discloses methods of manufacturing multilayered PCBs. In a particular method, individual layers are formed which include an overcoating of a partially cured polymer resin and solder bumps protruding through the overcoating. The solder bumps are formed on circuitry underneath the overcoating. The individual layers are subsequently compressed together and, through heat and pressure, the solder bumps and overcoatings on adjacent layers fuse together to create a polymer interlayer between adjacent layers with metal filled vias formed from the solder balls passing through the interlayer. Yamashita et al. also shows that the vias in the interlayer can be created from solder bumps that do not protrude through the overcoating on the individual layers which are used initially.